A superconducting wire has an electric resistance which converges close to zero at a certain temperature and has a high power transfer capability even at a low voltage.
In a superconducting cable having such superconducting wires, a cooling method performed using a refrigerant such as nitrogen and/or an insulation method of forming a vacuum layer is used to form and maintain an extremely low-temperature environment.
Tension or torsion may be continuously applied to a conventional superconducting cable when superconducting wires thereof are wound around a drum or the like while being spirally wound around an outer side of a former or the like to manufacture the superconducting cable or when the superconducting cable is bent in an installation section. The superconducting wire having a thickness of only about 0.1 mm may be broken due to stress such as tension or torsion. In particular, since a ratio of the costs of the superconducting wires in total costs of the superconducting cable is highest and thus the durability or physical reliability of the superconducting wires is required.
A former may be included at an innermost part of a core part of the superconducting cable. The former may include a plurality of element wires formed of a metal such as copper. By connecting the element wires of the former to the superconducting wires in parallel, the former may serve as a return circuit when fault current is generated in an electric power system of a superconducting system.
However, since general metal conductors are used as the wires of the former serving as the return circuit of the fault current, the former has a diameter greater than that of the superconducting wires and thus accounts for a greater part of the diameter of the entire superconducting cable.
However, a superconducting cable with superconducting wires having reinforced rigidity and capable of reducing the diameter of a former or the like has yet to be introduced.